Effects of Blaine and Tricalcium Aluminate on the Sulfate Resistance of Nanosilica-Containing Mortars

Abstract

This study set out to determine the effect of dry powder nanosilica (nS) on the sulfate resistance of mortars when paired with portland cements (PCs) of contrastingly different fineness and tricalcium aluminate (C3A) content. Several mortar mixtures containing incrementally higher cement replacement with nS were prepared with a lower-Blaine 4.1% C3A and a higher-Blaine 12.3% C3A PC. Similar mixtures for both cements containing microsilica (mS) were also prepared for comparison. Results indicated that microsilica increased sulfate resistance more effectively than nanosilica due to its superior dispersion in comparison to the agglomerated state of the nS. Poor dispersion of the dry powder nanosilica used in this study is suspected to increase mortar permeability and hinder the reported filler, paste, and interfacial transition zone (ITZ) densification effects of nS. Mortars made with a lower-Blaine and low-C3A cement paired with the agglomerated nanosilica exhibited more sulfate attack expansion in comparison to the control. Microsilica resulted in both pore and grain refinement of the mortar pastes. Increasing cement fineness proved beneficial in combination with either pozzolan regardless of the cement’s C3A content.